I'm wondering where the "forks" translation came from in the first place. Google Translate used to be fairly reliable for simple translations, but I've seen several examples in the last couple of years where it goes batshit crazy, including starting to loop hallucinating sentences on repeat. Is absolutely nobody checking how well it performs before deploying nowadays?
More seriously: Google Translate's bread-and-butter data source is documents that were human-translated from one language to another with high reliability (such as UN publications). That turns out to work remarkably well for building a neural net that can extrapolate how one sentence should translate to the same sentence in another language. But like most neural networks, it's vulnerable to garbage-in, garbage-out: much like you can get an animal detector to hallucinate "zebra!" if you feed it a noise-pattern as input, if you feed it character sequences that aren't actually words in the input language, it'll try to extrapolate what reality should be between all the corpus it's seen and you'll get garbage on the output side.
Since the tool doesn't actually know what words mean, it has no way, at present, to know "Yes" isn't a Spanish word (and as other commenters have mentioned, it may actually be "a Spanish word" in one weird context in one weird document somewhere in the corpus of all translated documents accessible from the Internet... Or some doc somewhere contains a close-enough typo in the Spanish input document that is over-reflected in the output because no other document contradicts the typo's apparent translation).